German Unexamined Application DE 39 18 990 also discloses a microscope with image brightness equalization. In a microscope, neutral density filters adapted to the objectives are introduced in the image beam path of the respective objective in the objective nosepiece, thereby achieving an image brightness equalization upon switching of the objectives. The neutral density filters are arranged on sliders, and can easily be removed from the objective nosepiece. It is disadvantageous that the neutral density filters are arranged on separate sliders, since they might easily be mislaid and/or be incorrectly inserted into the nosepiece.
German Unexamined Application DE 32 21 804 A1 discloses an illumination device for optical close viewing devices. In order to simplify handling for the viewer, provision is made for automatic brightness control as a function of the magnification that is selected. Various lenses with different magnifications can be introduced into the beam path of the illumination device, and brightness adaptation is brought about by way of a mask that has different openings. Depending on the magnification of the lens, a corresponding opening in the lens is introduced into the beam path in order thereby to achieve an adaptation of the brightness of the illumination device. The disadvantage of this apparatus is that further mechanical means must be provided in order to achieve synchronous switching between the lens and the mask opening.
U.S. Pat. No. 4,714,823 discloses an apparatus for determining the brightness in the image beam path of a microscope. A sensor is provided that determines the brightness in the image beam path of the microscope and delivers corresponding actuating signals to a lamp control system so that, for example, when an objective change is made the user is not surprised by excessively bright illumination in the image beam path. This apparatus once again, logically, requires further control means in order to adapt or control the brightness in the image beam path of a microscope. The design here cannot be described as simple.